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Manuscript Title: The evaluation of transition matrix elements for atomic excitations by a screened Coulomb potential.
Authors: A. Orban, B. Sulik
Program title: SCRMTRX
Catalogue identifier: ADRB_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 151(2003)199
Programming language: Fortran.
Operating system: Linux, UNIX.
RAM: 149K words
Word size: 8
Keywords: Screened Coulomb potential, Excitation, Transition matrix element, Ion-atom collision, Modified Bessel functions of half integer order, Derivatives of the modified Bessel functions of half integer order, Atomic physics, Other.
Classification: 2.6.

Nature of problem:
The electronic screening effect plays an important role in ion-atom collisions. Atomic or molecular transitions are often induced by the screened Coulomb potentials of atoms or partially ionized ions. The corresponding screening matrix elements are often required in theoretical descriptions. The SCRMTRX program calculates such screening matrix elements for bound-bound transitions for arbitrarily chosen target wave functions.

Solution method:
The calculation of the screening function is based on a multipole expansion series using the derivatives of the modified Bessel functions of half integer order. The program includes subroutines for calculating In+1/2(x) and Kn+1/2(x) and their derivatives in a wide range of n and x.

Restrictions:
The screening matrix element is considered as independent of the azimuthal coordinate of the internuclear distance.

Running time:
The calculation of the screening matrix element for a given internuclear distance is about 0.3s depending on the transition and the accuracy demands. The test calculations were made on a computer with 265 MB memory and a 800 MHz AMD processor.